Various operating aspects of robots have been known. In any robot of the articulated type, the polar coordinate type, or the cylindrical coordinate type, etcetera, wherein the driving joint performs a rotational motion among the various operation aspects, the operating regions of the robot are defined between the maximum and minimum operating angles along respective operating axes. The operable region of such robot within the combined operating regions results in a space of very complicated shape, and is often difficult for an operator to intuitively either visualize or understand.
A robot of the articulated type will be used as an example. The articulated type generally has three principal axes and a plurality of other axes around which its hands rotate. For instance, an articulated type robot has angular variation ranges based on three respective principal axes and angular variation ranges based on the two respective axes of a wrist. The movable region of the fore end of the wrist, which is based on the operations of the three principal axes among the aforementioned axes, defines a range of a spatially very complicated region.
In actuality, the movable ranges based on the two axes of the wrist are further superimposed on such region based on the three principal axes. Therefore, the motion of the point of the fore end of the wrist becomes more complicated, and a simple expression in two dimensions in nearly impossible.
Accordingly, the movable region of a robot of the type wherein the so-called driving joint performs a rotational motion, including the articulated type robot as stated above, cannot be immediately visualized by the operator. It is very difficult to conjecture beforehand the limits within which the point of the fore end of the wrist moves in case of actually operating the robot. With the prior-art control system of the robot, therefore, the fore end part of the wrist is moved to an unexpected position during the operation of the robot such as when in the teaching mode. This has undesirably resulted in the operator being endangered or the robot becoming damaged, although the operating speed is also a factor in such accidents.